Refrigeration with solid carbon dioxide



Jan. 2, 1934. F. HEYWOOD 1,941,744

REFRIGERATION WITH SOLID CARBON DIOXIDE Filed Jan. 25, 1953 I a) M ,r In k Han/72 Hgyumozl w, mmm

Patented Jan. 2, 1934 UNITED STATES PATENT OFFICE REFRIGERATION "WITH SOLID CARBON DIOXIDE Application January 25, 1933, Serial No. 653,534, and in Great Britain January 29, 1932 4 Claims.

When employing blocks of solid carbon dioxide evaporating into air for refrigerating two problems are commonly met with. Firstly, it may be difficult to secure a sufficiently rapid rate of 5 evaporation of the block to provide the desired cooling effect, as for instance in the case of refrigerated spaces of large size the walls of which are relatively poor heat insulators. Secondly it is difiicult to secure a uniform rate of evaporation during the life of the block since this rate is a function of the superficial area of the block, which decreases as increasing quantities of carbon dioxide are evaporated away.

These difiiculties may be overcome by using, instead of a single large blockf'a number of comparatively small blocks, or a block having a large surface to volume ratio, e. g. thin flat plates, but a considerable loss due to evaporation must occur in sub-dividing large blocks into such plates, while the handling of a large number of small pieces is a drawback.

According to the present invention, in a process of refrigerating with solid carbon dioxide evaporating into a current of air, a rapid and.

relatively uniform rate of evaporation is obtained by supporting the block on a number of horizontal heat-conducting bars, the edges of which in contact with the block are preferably sharp, so that as a result of the weight of the block and the evaporation at the surfaces of the heatconducting bars the block is slowly divided into a number of'separate slabs which depend between the bars. Means are preferably provided to cause the down draught of air which passes over the surface of the carbon dioxide to pass between the vertical slabs which are thus formed. In this manner the block is divided into a number of sections of relatively large superficial area without the loss of any refrigerating value outside of the system and since the further evaporation takes place chiefly at the sides of the slab thus formed, a substantially constant rate of evaporation is maintained.

In the accompanying drawing I have shown, more or less diagrammatically, my invention embodied in a refrigerating or cooling unit of a type adapted to be used in treating air, air being circulated through the unit. In the drawing,

' Fig. 1 is a view in sectional elevation of a unit embodying my invention, and

Fig. 2 is a view in sectional elevation taken along line 2-2 at right angles to Fig. 1.

As illustrated in the showing, element 1 is a heat insulated chamber provided with an ad- 85. justable damper 2 at the top. This damper may be slid laterally so as to establish communication of the chamber with the atmosphere to a greater or less degree, thereby adjusting the flow of air into and through the chamber. Within the chamber is mounted grid 3 composed of a plu- 0 rality of massive cutting bars made of aluminum or other good heat conductive metal; these bars having sharp edged tops. The chamber has a liner 4 shown as of heavy metal, forming a large radiating surface. Within the chamber, hori- 5 zontal plate 5 is also shown as of heavy metal I and having a thick edge, extending around three sides of the chamber and in good thermal contact with the liner. It is advantageous to make the liner, plate and the grid bars integral by 7 welding or otherwise, thereby facilitating passage of heat. The plate has an opening adapted to receive a block or brick of solid carbon dioxide.

Liner, platev and grid form a practically unitary structure, thermally speaking. With alu- 7 minum as the structural material, because of its high heat conductivity, local temperature differences are minimized. The plate is spaced away from one "side of the chamber leaving a free passage therebetween for circulating gases. Below the grid is a tray 8 which serves the double purpose of guiding circulating gases and of "collecting any liquid or frozen water which may form on the surface of the solid carbon dioxide and pass downward. A cock 9 is provided in the base of the tray to draw off water from time to time.

In using the apparatus, a block of carbon dioxide 6 is placed upon the grid. The drawing shows the apparatus after a block has been in position for some time, and partially consumed by evaporation. Warm air entering the chamber at the top imparts heat to the liner, and heat is thence transferred by means of plate 5 and the grid, to the block of dioxide. Because of the good interchange of heat between the massive grid, plate and liner, the grid bars are kept warm and they cut their way, so to speak, through the block. Evaporation is rapid at the surfaces of the solid carbon dioxide block adjacent the grid; 1 morerapid than from the surfaces exposed directly to the air. As the bars cut through the block, in the course of time it assumes the appearance shown with slabs 7 of solid dioxide hanging or depending below the grid between the bars.

Air enters the chamber through the top damper 2, passes between the block of solid carbon dioxide and the liner, below the grid, between the depending slabs of carbon dioxide, over the tray, and out the bottom. This flow is indicated by arrows in Fig. 2. Inspection of the figure shows that the total area of cooling surface, including the area of the block, the area of the liner, and the area of the several slabs, is large. Accordingly, a relatively small apparatus element suffices to cool a considerable volume of air passing through it. The carbon dioxide is renewed from time to time.

The chamber being heat insulated, as shown,

a wide range of evaporation rates can be obtained by varying the opening of the damper 2.

A refrigerating unit as described above was constructed with a grid consisting of eight parallel aluminum bars, 10.25 inches in length, 1 inch in depth and 0.25 inches in thickness. The bars were sharp edged at the top, the top edges meeting at an angle of degrees, and were spaced 1 inch apart. A block of solid carbon dioxide weighing originally 45 pounds was placed on the grid and observations were made of the weight of the block after regular periods of time. The results are given. in the following table and indicate the approximately uniform rate of evaporation of the block.

Time in Weight of hours block It will be seen that I have provided a compact, efficient apparatus for refrigerating by means of solid carbon dioxide. A large cooling area is afforded circulating air, by means of the unitary grid, plate and liner assemblage, and by means of the cutting up of the block of solid carbon dioxide into slabs by the grid. As a large brick becomes smaller more surface is developed. In an embodiment of the refrigerating unit shown and described, a grid was used little more than 8 by 10 inches in size, and the rest of the apparatus was correspondingly small; yet it allowed 35 pounds of solid carbon dioxide to evaporate uniformly in 12 hours; a very rapid rate of evaporation.

I claim:

1. A refrigerating unit comprising a heat insulated chamber having a heavy metal liner, 9. grid consisting of a number of spaced bars of good heat conducting material and having sharp upper edges disposed horizontally within said chamber and in thermal connection with the liner, said grid being adapted to receive and support a block of solid carbon dioxide and to allow the block to form, during evaporation, vertical slabs hanging between the bars, an inlet for air in the top of said chamber, an outlet for carbon dioxide gas and air at the bottom of said chamber, and means for causing a down draught of air in the chamber to pass between the vertical slabs of solid carbon dioxide below the heat-conducting bars.

2. A refrigerating unit comprising a heat insulated chamber, an inlet in the top portion for air, a sheet metal liner extending around the inside of said chamber, a grid consisting of a number of sharp-topped bars of good heat-conducting material disposed horizontally within said chamber, a heavy metal plate inside the liner, said plate and said grid being in thermal connection with said liner, the grid being adapted to receive and support a block of solid carbon dioxide, and to allow it to form, during evaporation, slabs hanging below the bars, the liner, plate and grid being so arranged that air entering the top inlet passes between the liner and the block, beneath the grid, between the slabs thus formed and out the bottom of the chamber.

3. A refrigerating unit comprising a heat insulated chamber, an adjustable air damper in the top thereof, a grid consisting of a number of sharp topped bars of good heat-conducting material disposed horizontally within said chamber said grid being adapted to receive and support a block of solid carbon dioxide and to allow the block to form hanging slabs below the grid, a horizontal plate in thermal connection with said grid and occupying the space between the block and three of the walls of the said chamber, leaving a passage between the block and the wall of the chamber opposite the ends of the bars, and a metal liner of good heat-conducting material in thermal connection with the grid and the plate.

4. The method of refrigerating by means of a chilled current of air and carbon dioxide, the latter furnished by a block of solid carbon dioxide evaporating into the former at a substantially uniform rate which comprises supporting the block on a plurality of spaced horizontal transverse bars having sharp-edged tops and bases of substantial width, said bars being composed of metal of high heat conductivity and being adapted to melt their way through said block, and passing air to furnish the chilled current above and around said block in down draft and through the spaces under the bases of the bars and,

thereby, between dependent unmelted slabs of dioxide passing through the interbar space.

FRANK HEYWOOD. 

